7.6.4. HV-04 — Advanced HTTP Server Features

This tutorial covers advanced server capabilities — static file serving, CORS, HTTP redirects, binary responses, custom headers and caching, content-type control, and status codes.

Prerequisites: HV-03 — HTTP Server Basics (basic routes and JSON).

7.6.4.1. Static File Serving

STATIC(server, path, dir) maps a URL prefix to a filesystem directory. All files under that directory are served with the correct Content-Type based on their extension.

// After server->init(port) but before server->start():
STATIC(server.server, "/static", "/path/to/public")

Important

STATIC must be called after init() (which registers the HTTP service with the router) and before start().

Clients can then fetch /static/index.html, /static/style.css, etc.

7.6.4.3. HTTP Redirects

REDIRECT(resp, location, status) sends a redirect response:

GET("/old-path") <| @(var req : HttpRequest?; var resp : HttpResponse?) : http_status {
    return resp |> REDIRECT("/new-path", http_status.MOVED_PERMANENTLY)
}

Common redirect status codes:

http_status.MOVED_PERMANENTLY (301) — permanent redirect, browsers cache it
http_status.FOUND (302) — temporary redirect

7.6.4.4. Custom Response Headers and Caching

Use set_header on the response to add cache-control, ETags, and custom application headers:

GET("/cached") <| @(var req : HttpRequest?; var resp : HttpResponse?) : http_status {
    set_header(resp, "Cache-Control", "max-age=3600, public")
    set_header(resp, "ETag", "\"v1.0\"")
    set_header(resp, "X-Server", "daslang")
    return resp |> TEXT_PLAIN("cached response")
}

7.6.4.5. Binary Response

DATA(resp, data, length) sends raw bytes with Content-Type: application/octet-stream:

GET("/binary") <| @(var req : HttpRequest?; var resp : HttpResponse?) : http_status {
    var payload = "BINARY\x00DATA1234"
    return resp |> DATA(payload, 16)
}

7.6.4.6. Content-Type and Status Codes

set_content_type(resp, type) give full control over the response:

// HTML response
GET("/html") <| @(var req : HttpRequest?; var resp : HttpResponse?) : http_status {
    set_content_type(resp, "text/html")
    resp.body := "<h1>Hello from daslang!</h1>"
    return http_status.OK
}

7.6.4.6.1. Non-200 JSON Responses

JSON() and TEXT_PLAIN() accept an optional status parameter (defaults to http_status.OK):

GET("/not-found") <| @(var req : HttpRequest?; var resp : HttpResponse?) : http_status {
    let payload : tuple<error:string; code:int> = ("resource not found", 404)
    return resp |> JSON(write_json(JV(payload)), http_status.NOT_FOUND)
}

7.6.4.6.2. 201 Created with Location Header

POST("/items") <| @(var req : HttpRequest?; var resp : HttpResponse?) : http_status {
    set_header(resp, "Location", "/items/42")
    let payload : tuple<id:int; body:string> = (42, string(req.body))
    return resp |> JSON(write_json(JV(payload)), http_status.CREATED)
}

7.6.4.6.3. 204 No Content

POST("/ack") <| @(var req : HttpRequest?; var resp : HttpResponse?) : http_status {
    return http_status.NO_CONTENT
}

7.6.4.7. Quick Reference

Function	Description
`STATIC(server, path, dir)`	Serve static files from directory
`allow_cors()`	Enable CORS headers on all routes
`REDIRECT(resp, location, status)`	Send 3xx redirect response
`JSON(resp, json_str, status?)`	JSON response (default 200)
`TEXT_PLAIN(resp, text, status?)`	text response (default 200)
`DATA(resp, data, length, status?)`	Binary response (default 200)
`set_header(resp, key, value)`	Set response header
`set_content_type(resp, type)`	Set Content-Type header